Mixed-phase clouds, which can exist days even weeks, are frequently observed in the Arctic region where they play an important role in the radiation balance. Observations also show that ice particles precipitate from these clouds nearly all time. The question of whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model, and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power law relationship with ice number concentration (ni). wi and ni from a LES cloud model with stochastic ice nucleation also confirm the 2.5 power law relationship. The prefactor of the power law is proportional to the ice nucleation rate, and therefore provides a quantitative link to observations of ice microphysical properties. Figure 1 shows LES results for two ice nucleation rates: Blue points correspond to low ice nucleation rate and red points to high ice nucleation rate. It’s clearly to see that points follow the 2.5 power law as our analytical model expected. The intercept shift predicted by the minimalist model is 1.05, which is very close to the best fitted line shift in Figure 1, 5.77-4.75=1.03. This provides a compelling link between ice microphysical properties and the ice nucleation rate within the cloud, which may be used in future analysis of cloud observation.

Dr. Bhabana Pati visited the department on Friday, July 12, 2013. Bhabna graduated in 1997 with a Ph.D. after working with Dr. Jacek Borysow as a “laser junkie.” She developed the single mode tunable titanium sapphire laser and subsequently tunable ultraviolet laser via sum frequency generation in a non-linear crystal.

Today she is a principal scientist at Q-Peak Co. and still a “laser junkie,” trying among many other things to shoot lasers at the Moon to find out its composition via Laser Induced Breakdown Spectroscopy.

Associate Professor Claudio Mazzoleni (Physics) and his graduate student, Swarup China, published an article in the journal Nature Communications on the structure and properties of soot produced by biomass burning.